Lead-based paint

“ The paint for a job stands mixed over night; the painters fill their pots from time to time during the day, but never stir the paint from the bottom, hence the last pot or two filled will have all the coarse pigment of the batch. There are cases, I admit (too many of them) , where not only white lead, but dry colors and colors in oil, are too coarse to work well, but the best white lead and heavy colored pigments in oil or turpentine are liable to be called sandy unless frequently stirred by the painter. ”

“ White lead is used more than any other substance for paint, although zinc white has come into considerable use in the last few years. No other nation uses lead paint to such an extent as does the United States, partly because no other nation could afford so general a use of such an expensive material, and partly because so many wooden buildings are erected. By using brick, stone, or cement, of which we have practically an unending supply, to take the place of wood, our store of which is rapidly disappearing, we could avoid much of the drain on our mineral resources which are used for paint. ”

“ Paint films made of certain inert pigments, when tested on the filmometer, were relatively high in strength, but relatively low in elasticity. Such pigments, when used in large percentage, form coatings which are hard and apt to crack. The use, however, of these pigments in moderate percentages seems very beneficial in overcoming the effect of using an excessive percentage of white lead, or of zinc oxide. ”

“ As to the relative cost of iron oxide paints and red lead, there is no doubt that the first cost of painting structures with iron oxide is somewhat less than with red lead. The best railroad authorities state, however, that labour in painting structural work costs twice as much as material. The true economy must therefore be sought in the durability of the paint as well as the preservation of the structure from rust. Actual experiments have shown that structures painted with iron paint had to be repainted in the third or fourth year, those with red lead not until the sixth year. ”

“ Every painter has his own peculiar way. In nearly all cases, the simplest plan is to use pigments ground in oil instead of dry powders. With a pallet knife break up the lead rather stiff, adding a little oil. Thin down each paint until it is rather stiffer than the whole will be when ready for actual application, or if dry pigments be used, add a little oil, and thoroughly mix. The lead, zinc, or other base being ready, add some pigment, and well stir. ”

“ For ordinary quantities of paint, of which white lead forms the base, the following is the method usually employed. It will be understood that the paint consists of a base such as white lead, linseed oil, either raw or boiled, driers—either patent or liquid—and turpentine. A can or kettle is most usually employed for mixing the white lead in, and this is first thinned out and mixed with the driers and oil, the colour being afterwards added to it. A little oil is first placed in the can, which is twisted around so that the oil covers every part of the inside surface. ”

“ There is nothing more variable in quality than paint, and even experts are puzzled at times and it is necessary to have a chemical analysis in order to determine between good and bad.
For exterior use the proper kind should be a mixture of pure white lead and linseed oil or pure zinc white and linseed oil. Manufacturers, more especially those of white lead paints, will insist that theirs is the only kind to use, and the zinc paint producers will do likewise, but a reliable dealer or architect will inform you correctly. ”

“ The ingredients for making about 40 pounds of best paint for indoors, tinted to a French gray color, would be 28 pounds of genuine white lead, 3 pounds of patent driers, about 1⁄2 gallon of raw linseed oil, and 1 quart of turpentine. Mix up the lead and driers with a broad stick to the consistency of a thick paste, using linseed oil. If all is to be tinted one color, for French gray add a little ultramarine blue and either a little Venetian red or lamp black. If a warm gray is wanted, add the red, if a cool metallic tint, add the black. The ultramarine can only be bought in powder ”

“ Possessed of extreme stability, it finds wide use as a constituent of paints and as a base for tinting colors. The photomicrograph of this pigment shows its extremely fine, amorphous nature with complete absence of crystals. In fineness it closely approaches zinc oxide. On account of its non-poisonous properties it is replacing corroded lead in many places. Unified paints containing sublimed white lead are of great value, showing upon long exposure very little decay. ”

“ Great as is the opacity of white lead, it is apt to lose that property in some measure in course of time, and become more or less transparent. If, over a series of dry oil-colour rubs of varied hues, there were brushed sufficient white lead paint to utterly obscure them, after some years those rubs would indistinctly appear, and by degrees become more and more visible, until at last their forms—if not their very colours—could be recognised. ”

“ This pigment has the property of forming with linseed oil a hard elastic coating, clinging with great tenacity to the metal. It has no oxidising effect on iron, and does not act as a carrier of oxygen from the atmosphere after the paint has set, neither does it render the oil brittle nor promote rust. When red lead fails, it is principally by gradual wear or friction from the outside. It does not scale or blister, which both asphalt and iron oxide paints will do, thereby requiring a thorough scraping and removal of old material before a new coat can be applied. ”

“ Good white lead is a dense, perfectly amorphous powder of perfect whiteness, possessed of great body and covering power when combined with oil. When mixed with linseed oil and used as paint it rapidly dries in the air and assumes a varnish-like, glossy, hard surface, and is capable when once dry of resisting the action of air and water for any length of time. It does not weep when laid on a surface with a brush, that is, the oil does not separate from the solid material of the paint. ”

“ Every painter has seen (the result too of unpardonable negligence) plates of glass so covered with spatters, that to remove them would require more time than would serve to paint the woodwork of a “full-trimmed” window.
In priming work which is to be finished in oak, finely-ground French ochre is recommended. The objection to this pigment, that it does not work smoothly and easily under the brush, has arisen from its coarseness. Finely ground in boiled oil, it works as smoothly as white lead, and makes an excellent foundation for the succeeding coats. ”

“ No washing or drying is necessary. No women are engaged in the manufacture, and but few men. The white lead thus produced by the aid of electricity is deposited in a peculiar state of disintegration, it is perfectly amorphous and non-crystalline, of the purest quality; its density is 5·8. When ground in oil and made into paint, it possesses great body and a covering power inferior to no other paint, if not superior to them all. ”

“ That is to say, the pigments are mixed with an oil from which the impurities, and the natural yellow and red colouring matter, have been removed, so that the colour of the paint is white. If ordinary oil be used, the paint is more or less yellow. In order to render such paint quick drying, a certain amount of dryers, in a solid or liquid form, is added. These dryers almost invariably contain lead, so that zinc white paint is contaminated by lead in another way, which may not be suspected, or which is overlooked. ”

“ There are several formulas in circulation for the mixing of the lead, but the writer thinks the one here given (used in the leading factory paint shops) covers the painter's practical needs fully. Mix dry white lead to a grinding consistency in 3/4 raw linseed oil to 1/4 japan, the liquids to be carefully measured. Add enough lampblack to give the mixture a clean slate color, then run through the paint mill, after which reduce to a brushing consistency with the proper proportions of oil and japan. Make the lead just stiff enough to brush on with a fairly stiff bristle brush. ”

“ To obtain a white lead of excellent quality for its various uses, it is necessary to produce a substance which possesses sufficient body to cover surfaces to which it may be applied as paint, and it must possess sufficient base to combine with the oil of the paint to form a vehicle or varnish to retain and hold the body on the surface. This is found to be the case with sub-carbonate of lead, or especially with a compound constituted of two or three equivalents of carbonate of lead, with one equivalent of hydrated oxide of that metal. ”

“ The principal consumption of white lead is for paint; to produce this paint it is ground with oil in varying proportions, about 8 to 15 per cent. This produces the ordinary white lead in oil, and is worth from 19l. to 20l. a ton, but often more than this amount.
Dry powdered white lead is chiefly made for and used by grinders and mixers, who combine with it a variety of other cheaper materials—chalk, clay, sulphate of lime, and sulphate of baryta, but principal use is made of chalk and barytes. ”

“ The careful painter will, when using heavy pigments, carry a paddle, and not neglect to use it. To prevent white lead and other heavy pigments from settling in the pot the paint must be well mixed, and kept mixed by stirring with a paddle as often and as much as may be necessary to keep the oil or other vehicle, and the pigment well incorporated. No one out a novice, or a careless painter will permit a sediment to accumulate in the bottom of his pot; no matter whether the pigment is coarse or fine; or whether the vehicle used is linseed oil, turpentine or benzine. ”

“ Oil paints are made up of four parts—the base, the vehicle, the solvent and the driers. Pigment may be added to these to obtain a paint of any desired colour.
There are several bases for oil paint, those most commonly used for building work being white lead, red lead, zinc white and oxide of iron. White lead is by far the commonest of bases for paint. When pure it consists of about 75% carbonate of lead and about 25% of lead hydrate. It is mixed with 6 or 7% by weight of pure linseed oil, and in this form is supplied to the painter. ”

“ To mix 1 pound of ordinary oil paint, take about 8 ounces of pigment the desired color. White lead for white, light grays, pinks, cream, etc., Venetian red or vermilion for red, and so on, according to the color desired. Add to this about 2 ounces of liquid driers, then make up to 1 pound with either linseed oil alone or oil and turpentine in equal parts. Remember, the more oil, the more driers is advisable, but never less than 1 part driers in 8 or 10 of entire bulk. If only small quantities of paint are wanted, that sold ready mixed would be cheapest and would do for ordinary inside work. ”

“ Never glue hot wood, as the hot wood will absorb all the water in the glue too suddenly, and leave only a very little residue.
Inert Pigments. An inert pigment is one which, when mixed with oil, will have no chemical action upon it. It will have no chemical effect upon any other substance with which it is mixed, as for instance barytes, silica and gypsum. On the other hand, white lead, Prussian blue, and chrome yellow, are chemical colors, and are supposed to chemically affect the oil and some other pigments.
Killing the Smell of Paint. ”

“ A sufficient quantity of oil and the patent or other driers is then added. The most convenient implement for actually mixing the paint is a broad piece of wood shaped like a narrow spade, or a spatula may be employed. The lead is stirred and beaten against the sides of the tin until the whole is of the same consistency, and more oil is added until the thickness is not sufficient to support the stick standing upright. Turpentine may now be added to further thin the mixture, and then the colour is added. ”

“ In this way the red lead and oil get their initial set on the surface of the iron, and the closer the pigment is brought to the iron the more durable will it be found. Some parties prime iron with iron oxide paint or metallic brown before applying red lead, which appears to be a mistake, as this paint readily scales from iron, and, of course, carries the lead with it. Others coat the iron with oil before applying the red lead. ”

“ On account of its alkaline nature, this pigment acts upon the saponifiable oil in which it is ground, forming lead soaps which [44] accelerate chalking of white lead—the greatest evil attending its use. Solubility in carbonic acid of the atmosphere and decay in the presence of sodium chloride may be active causes of the rapid chalking of this pigment at the seashore. Checking in some climates appears to proceed rapidly on white lead paints, in a deep hexagonal form, leaving a series of rough crests and cracks. This checking is secondary to the chalking which takes place. ”

“ Properties of White Paint.—As the result of hundreds of experiments in carbonate of lead and hydrate of lead, both separately and mixed, Messrs. Wigner and Harland, of the British Society of Public Analysts, reach the conclusion that a white paint, to be efficient, and to possess both the powers of laying on readily and easily, and by its opacity hiding the color beneath, must consist of an admixture of hydrate and carbonate of lead in a certain definite proportion. ”